The present invention concerns stabilization of polyether polyols and polyester polyols and the use of the stabilized polyols in the preparation of polyurethane foam. In particular the invention relates to stabilization of polyols with benzotriazole stabilizer compositions and the color or scorch inhibition of flexible, semiflexible and rigid polyurethane foams made from the stabilized polyols.
In the production of polyurethane foam from polyether polyols and polyester polyols, discoloration or scorch occurs during processing and production of the foam in the form of slabs, buns or other shapes. The foam becomes scorched under certain reaction conditions and severely degrades the physical properties of the product. The scorch manifests as discoloration at the center of the bun and can range from slight yellow to dark brown, rendering the foam unsuitable for commercial use. Furthermore, some bun foams become discolored or scorched when removed hot from the production line and stored in stacks due to heat dissipation from the center of the stack.
To prevent discoloration during processing and storage, scorch inhibitors are added to the polyol. Scorch inhibitors prevent degradation of the foam during the exotherm curing step when most of the degradation takes place, as well as during storage of the foam.
Prior art discloses the use of aromatic amine type scorch inhibitors, as for example in U.S. Pat. No. 3,637,865. Some commercial aromatic amines contain free amine which is liberated during processing of the polyol and, even in low quantities, is undesirable in the workplace atmosphere because of worker health and environmental considerations.
Aromatic amine scorch inhibitors are employed in conjunction with other stabilizers such as triesters of 1,3,5-tris(2-hydroxyethyl)-s-triazinetrione disclosed in U.S. Pat. No. 4,228,247.
Surprisingly, it has been discovered that certain benzotriazole compounds enhance the oxidative stability of polyether polyols and polyester polyols and furthermore, provide good scorch inhibiting properties to polyurethane foam. Moreover, benzotriazole and its alkyl derivatives can be combined with aromatic amines in relatively low ratios to form synergistic scorch inhibitors.